In the related art, a method of using a paper medium has been used as means of reading a document. Meanwhile, through performance improvement of a computer or development of the internet, a chance of reading an electronic medium document is increased. As an advantage of using the paper medium, it is possible to read it in a large size and to grasp the entire sentences by looking down, and it is inexpensive. On the other hand, as an advantage of using an electronic medium, it is possible to display moving image, such that in internet or video, and it is easy to carry. Accordingly, a new interface which takes advantage of the paper medium of the related art and which is for improving utility value of the document by linking to the electronic medium has been developed.
The above-described interface has a function of displaying additional information related to a paper medium document obtained by capturing the paper medium document placed just in front of the user, by using a camera fixed to an arbitrary place or a freely movable camera. Here, as a technology of displaying the additional information, an information presenting method that is performed by augmented reality (AR) which overlaps with and displays the additional information on the paper medium document or on a document that is projected has been proposed in recent years. By the information presenting method, it is possible to associate the additional information with a display position on a text image, and to link the electronic medium to the paper medium.
Furthermore, a technology also has been developed in which annotation information or the like that is additional information is displayed so as to overlap with the paper medium document, the user performs an interaction operation with respect to the annotation information, thereby realizing work support of the user. For example, an augmented reality technology that presents annotation or the like associated with a real object by projecting an overlapped image including the additional information that is a virtual image, using a projector with respect to the real object such as the paper medium document or the like, is disclosed.
In the above-described augmented reality technology, correctly calculating a position of a finger of the user in a world coordinate system (in three dimensions) using the camera fixed in an arbitrary place or the freely movable camera is desired. A binocular stereo method is known as a general method for calculating the position of the finger in the world coordinate system. The binocular stereo method is used to calculate a distance between an arbitrary reference point and a target object according to the principle of triangulation, using position shift (parallax) of an image occurring when the same object (target object) is captured by two cameras which are in parallel with each other and a positional relationship of which is known. A technology regarding the binocular stereo method is disclosed in, for example, “Shimizu, Fujiyoshi (Chubu University), “Study on high speed three-dimensional position estimation using multiple asynchronous cameras”, 2005”.